Plastic films mounted with pressure sensitive adhesives are used in the automobile industry to add styling features to automobiles. Such films may be pigmented internally, printed and top coated or, alternatively, layered to simulate the appearance of a glossy base coat/clear coat paint finish. Plasticized polyvinyl chloride (PVC) has been used for many years as the polymer building block for the decorative film. Scotchcal, manufactured by 3M, is a typical example. In production, the plasticized PVC is either clear or pigmented to match color requirements and cast as a platisol or organosol onto a casting medium and passed through a drying oven to remove residual solvents and to fuse the composition into a continuous film. In a second process, an acrylic pressure sensitive adhesive is coated from solvent onto a silicone coated release liner and advanced into a drying oven for solvent removal followed by lamination to the cast PVC. The casting base used for producing the PVC film is removed either in-line or in a post operation. The PVC film can then printed and/or top coated and/or die cut into desirable shapes to meet the design requirements.
However, the use of PVC in the conventional plastic film described above creates a number of problems. In recent years consumer demands have increased in both visual and performance requirements and environmental regulations have become more stringent. PVC chemistry cannot meet the extended weathering requirements that the automobile industry is currently seeking. Additionally, the automobile industry is turning away from the use of chlorine-containing materials due to a number of environmental concerns. Also, plasticizers used in the formation of PVC polymers tend to migrate into and through adjacent layers as the plastic film ages. Migration of the plasticizers into the pressure sensitive adhesive layer can lead to reduction in the adhesive bond. Similarly, migration of the plasticizers into the clear coat layer can lead to delamination or loss of surface gloss. Finally, PVC paint films lack the high gloss "paint-like" appearance that is desirable in the automobile industry.
Dissatisfaction with use of PVC polymers has led to attempts to improve performance and appearance of the decorative sheets used to surface automobile body panels. An example of such an attempt is U.S. Pat. No. 5,518,786 (Johnson '786). The Johnson '786 patent discloses a multilayered plastic film wherein the clear coat layer is comprised mainly of a weatherable optically clear polymer containing a fluorocarbon resin and an acrylic resin. The use of such a clear coat yields the desired weatherability and a high gloss/Distinctness of Image (DOI). The Johnson '786 patent further discloses a method for further enhancing the DOI by coating the pressure sensitive adhesive onto a polyester film. However, the Johnson '786 patent is deficient regarding environmental and recycle issues because the base coat is composed of one or more plasticized PVC polymer layers. Plasticizer migration may also effect the long term performance of the Johnson '786 paint film.
To be suitable for exterior automobile use, a paint finish must meet automobile manufacturer's durability standards as well as standards of visual appearance. One important test of visual appearance is referred to as DOI. DOI is a measurement of the clarity of an image reflected by the finished surface. DOI can be measured by any of a number of instruments including the Dorigon Gloss Meter manufactured by Hunterlab, the QMS-BP manufactured by Autospect, and the GLOW-BOX manufactured by I.sup.2 R. Weatherability of the finish, measured in part by UV resistance, is also an important factor. In addition, the paint finish must exhibit sufficient elongation at room temperatures to enable application and repositioning of the paint finish to three-dimensional complex substrate surfaces.
Therefore, there is a need in the art for a plastic paint film for application to contoured exterior car body members or panels having both the durability and appearance properties necessary for exterior automobile use and possessing the room temperature elongation necessary to be hand applied and repositioned. In addition, there is a need in the art for a plastic paint film that does not contain PVC polymers.